There are electronic components that require hermetic enclosure, including, for example, piezoelectric resonator devices, such as a crystal resonator, a crystal filter, a crystal oscillator and the like. In each product, a metal thin film electrode is formed on a surface of a crystal resonator plate, and the crystal resonator plate (specifically, the metal thin film electrode) is hermetically enclosed so as to protect the metal thin film electrode from ambient air.
Since components are typically surface-mounted, these piezoelectric resonator devices are increasingly often hermetically accommodated in a package made of a ceramic material. For example, Patent Document 1 discloses a configuration which includes a base (mounting substrate) having a crystal resonator plate mounting portion, and a lid (cover) having an inverted U-shaped cross-section, where a package made of a ceramic material that hermetically encloses the base and the lid is mounted on a circuit substrate and joined thereto using a conductive adhesive material, such as solder or the like.
In a conventional piezoelectric resonator device, a terminal electrode is formed on a bottom surface of the base. The terminal is extended from the bottom surface to a side surface of the base by a castellation formed on the side surface of the base so as to confirm a connection state depending on the migration of solder (conductive adhesive material).
Incidentally, for a circuit substrate on which a conventional piezoelectric resonator device is mounted, a so-called glass epoxy substrate is widely used, which is obtained by impregnating a glass fiber mesh with an epoxy resin material. The glass epoxy substrate is advantageous in terms of machinability and cost. Also, a solder paste is applied on an electrode pattern of the circuit substrate using screen printing or the like. Thereafter, the piezoelectric resonator device package is mounted on the circuit substrate with the terminal electrode of the piezoelectric resonator device package being overlaid on the electrode pattern of the circuit substrate. The solder paste is melted in a melting furnace (a heating furnace, etc.), so that the piezoelectric resonator device is joined to the circuit substrate by the solder.    Patent Document 1: JP 2002-76813 A